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Minimal data are available on protein requirements throughout the lifespan. Currently available recommendations are based on nitrogen balance data. The limitations of the nitrogen balance method have been well described. Importantly, nitrogen balanced underestimates requirements.

The current dietary reference intake (DRI) requirement for healthy adult males is based on the reanalysis of the nitrogen balance date from Young and Scrimshaw. This data was reanalyzed statistically by Rand et al. and he concluded that the protein requirement of healthy adults was 0.65 and 0.83 (mean and RDA) g/kg/day of good quality protein. Using IAAO, our group estimated the protein requirement of young men (mean age 27 years) to be 0.93 and 1.2 g/kg/day (mean and RDA).

Currently there are no studies on protein requirement in the elderly. In a recent nutrition survey conducted by national health and nutrition examination survey (NHANES), the authors concluded that adults between the ages of 51 - 70 years old consumed an average on 1.0 g/kg/day (ideal body weight) of protein which represents about 15 % of calories. Depending on the calculations used for ideal body weight some older adults could be getting higher or lower than requirement. There is no scientifically derived protein estimate for older adults. Therefore there is a need to measurer protein requirement in that population.

The goal of this study therefore is to measure the protein requirement of male elderly subjects > 75 years using the indicator amino acid oxidation (IAAO) technique.

Hypothesis:

The investigators hypothesize the protein requirement in elderly male subjects will be lower (0.85-1.05 g/kg/day) than that established in young healthy males ( 0.93 - 1.2g/kg/day).

On the study day, the diet will be provided as free amino acids, with calories made up by a liquid diet and protein free cookies. Protein intakes will be varied as 0.2, 0.5, 0.7, 0.9, 1.0, 1.2, 1.5, 1.8, 2.0 g/kg/day.

Breath samples will be collected on day 3 of the experiment between the 4th and 5th meal and after the 6th and 7th meal. The ratios of carbon 13 to carbon 12 will be measured in breath. [ Time Frame: 10 months ]

Secondary Outcome Measures
:

Urine samples will be collected on day 3 of the experiment between the 4th and 5th meal and after the 6th and 7th meal for measurement of the rations of the enrichment of carbon 13 to carbon 12 in urine phenylalanine. [ Time Frame: 10 months ]

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